One of the things I love about my job is the endless opportunities to learn new things. I have to try to keep up-to-date in the areas of biology that I teach about, & this means a lot of reading & talking with people. But the opportunities are much wider than that – when I was developing the Science on the Farm website, I started learning about technology, soil science, all sorts of stuff (& I loved it). But today it was biology – I found out that E. coli can taste things!
This was via my current lunch-time reading: Microcosm, by the most excellent science writer, Carl Zimmer. (It has been suggested to me that the subject of intestinal bacteria isn’t perhaps ideal for looking into while eating…) Anyway, one of the topics he touches on is the way that E.coli moves around.
E.coli can get around using flagella – long, hair-like structures that project through its cell wall and spin like propellors. It moves in a series of brief, random runs, separated by tumbles – each tumble sets the bacterium facing in a new direction. And it can home in on ‘attractive’ chemicals, eg the amino acid serine, using nothing more than these runs & tumbles. As long as the bacterium is moving towards a serine source (ie in the direction of increasing concentration), each ‘run’ is longer. If a tumble points it away from the serine source, the next run is shorter. But how does something as simple as a bacterium know which way to go?
Well, first of all, E.coli isn’t really all that simple: Zimmer’s entire book points out time & time again what a complex little organism it is. And as for the control of runs & tumbles – it turns out that E.coli has a sense of taste. At the tip of an E.coli cell, thousands of sensory proteins project through its cell membrane – Zimmer likens them to a ‘microbial tongue’. There are five types of these cellular sensors, and when they detect a particular molecule, such as serine, this sets off a communication cascade within the cell. If they measure a rising concentration of serine, the flagella will beat for longer before a tumble, and the bacterium moves towards the serine source. If the serine levels drop because a tumble has left the bacterium facing away from the source, tumbles come more frequently until a random swerve puts the organism back on track for serine once more.
That is so neat 🙂 I knew that E.coli could move around, towards or away from various stimuli, but I had no idea how it detected them. Another day, another new idea!
C. Zimmer (2008) Microcosm: E.coliand the new science of life. Pantheon